Hillary Clinton, a fixture on the American political scene for a generation, is set Thursday to accept the Democratic presidential nomination and then tell Americans why they should trust her to be the new American leader when President Barack Obama leaves office in January.

Clinton, the first U.S. woman to become a major party's presidential nominee, is the country's most admired woman, according to Gallup. Yet a majority of U.S. voters at the same time tell Gallup they do not trust her, conflicting views that have left her locked in a tight contest with Republican presidential candidate Donald Trump for a four-year term in the White House.

Trump regularly calls the Democratic nominee “Crooked Hillary,” who lied to the American public about her missing emails, and whose status as a longtime politician has made her beholden to campaign contributors.

The 68-year-old Clinton, Obama's secretary of state from 2009 to 2013, appeared briefly with him Wednesday on stage at the Democratic National Convention In Philadelphia, Pennsylvania, after he delivered a ringing endorsement of her as his successor. He said no man or woman had ever sought the U.S. presidency who was more qualified than she is, including him or her husband, former President Bill Clinton.

On Thursday, it is Clinton's turn to make her own case. Ahead of her speech, campaign manger Robby Mook, said she would "lay out very clearly the choice that people face" in the November 8 election.

Mook acknowledged to the "CBS This Morning" show that Trump, a real estate mogul making his first run for elective office, "is making a lot of really big promises and some people find those attractive."

"What we need to do as a campaign and what Hillary is going to do tonight and what we've done at this convention is make sure people know the facts," Mook said. He described Trump as "someone who every turn of his life has made more money, become more famous at the expense of working people and folks need to understand that."

A supporter of former Democratic Presidential candidate Senator Bernie Sanders sits in the the media center after walking out of the convention in protest after Hillary Clinton was nominated during the Democratic National Convention in Philadelphia.

Earn voters' trust

Clinton has said on numerous occasions that she needs to earn voters' trust, shaken in part because of her use of a private, unsecured email server while she was the country's top diplomat during Obama's first term. She said she used the private server rather than a more secure government server because it was more convenient for her. The U.S. Federal Bureau of Investigation recently concluded that she was "extremely careless" in her handling of classified material contained in her State Department emails, but that no criminal charges were warranted.

Mook said the quadrennial Democratic convention has served as a testimonial for her candidacy, with "people speaking about how they know they can trust Hillary because she has always delivered for them."

Obama was her chief booster Wednesday night, to the roaring cheers of thousands of convention delegates.

"This year, in this election, I'm asking you to join me -- to reject cynicism, and reject fear, and to summon what's best in us; to elect Hillary Clinton as the next president of the United States, and show the world we still believe in the promise of this great nation," Obama said.

President Barack Obama and Democratic Presidential candidate Hillary Clinton wave together during the third day of the Democratic National Convention in Philadelphia , July 27, 2016.

Preparing to be president

He said nothing truly prepares a person for being president, but contrasted Clinton's experience with that of Trump, a one-time television reality show host who as a developer has built New York skyscrapers and casinos along the Atlantic Ocean.

"Until you've sat at that desk, you don't know what it's like to manage a global crisis, or send young people to war," Obama said. "But Hillary's been in the room; she's been part of those decisions. She knows what's at stake in the decisions our government makes, what's at stake for the working family, the senior citizen, the small business owner, for the soldier, for the veteran."

The crowd in Philadelphia booed when Obama mentioned Trump, to which Obama replied, "Don't boo, vote."

He said last week's Republican convention presented no serious solutions, but instead fanned "resentment, and blame and anger and hate." And he seized on Trump's statements suggesting he would insist NATO allies have fulfilled financial responsibilities before the U.S. would come to their aid.

"He cozies up to (Russian President Vladimir) Putin, praises Saddam Hussein, tells our NATO allies that stood by our side after 9/11 that they have to pay up if they want our protection," Obama said. "Well, America's promises do not come with a price tag."

Republican presidential candidate Donald Trump speaks during a news conference at Trump National Doral, July 27, 2016, in Tampa, Fla.

Trump fires back

Trump fired back at the largely optimistic tone of Obama and other Democratic speakers who this week have taken exception to Trump's campaign slogan pledging to "Make America Great Again."

"Our country does not feel 'great already' to the millions of wonderful people living in poverty, violence and despair," he wrote on Twitter.

Trump's campaign issued a statement calling Wednesday a "sad night" for the Democratic Party and saying they presented only proposals to reward the rich while attacking "decent Americans who want change for their families."

"They offered no solutions for the problems facing America -- in fact, they pretended those problems didn't even exist." the statement said.

Along with Obama, other Democratic speakers lashed out at Trump, with Vice President Joe Biden questioning the billionaire's commitment to the middle class.

"He is trying to tell us he cares about the middle class. Give me a break. That is a bunch of malarkey," Biden said.

Clinton's vice presidential running mate, Virginia Senator Tim Kaine, said, "Our nation, it is just too great to put it in the hands of a slick-talking, empty-promising, self-promoting, one-man wrecking crew."